Use of inorganic fiber as a binder in a pelletized ore



United States Patent 3,151,972 USE {3F INGRGANIC FIBER AS A nnmnn EN A PELLETHZED SEE William C. Streib, North Plainfield, Ni, aseignor to Johrm-Manville Corporation, New York, N.Y., a corporation of New York No Drawing. Filed Oct. 28, 1958, Ser. No. 830,174 5 (Cl. 75-5) The present invention relates to a method of pelletizing ores and more particularly to an improved method or" pelletizing or balling iron oxide ores such as taconite ore concentrates and the pelleted iron oxide products thereof.

Rapid depletion of high grade iron and like ore reserves in the United States and thus greater dependency upon foreign ore deposits has instigated mining and metallurgical organizations to seek new means of improving and utilizing readily available lower grades of ore. Taconite ores, for example, provide a potential and plentiful source of low grade iron ore Within the continnent but typical taconite ores contain only approximately 30% iron which is too low for economical recovery under normal conditions. Moreover, such low iron content ores require substantial up-grading to about 60 to 65% iron content. Up-grading techniques for low iron content ores such as taconite ores may comprise, among other methods, grinding and chemically reducing the hematite in the taconite ore to magnetite by hot reducing gases and slurrying the magnetite whereupon magnetic separation procedures are utilized to separate or concentrate the iron fraction. Recoveries of approximately 60% concentrate are obtainable after grinding to essentially minus 325 mesh. The final magnetite or other concentrate resulting from such techniques however is too fine in form (about 325 mesh) for use in normal blast furnaces and, for the most part, would be lost in the stack gases. Moreover, such fine particles are also too fine to be sintered directly by conventional techniques.

The common practice of utilizing magnetite or the like concentrate fines has been to pelletize the same by moistening the fines, adding a binder such as bentonite clay and forming pellets or balls in a rotary drum. These pellets or balls are partially dried and then fused at about 1800 F. typically by passing them through a furnace which sinters the same to form hard, compact and dense pellets which are easily handleable and may be charged into a blast furnace for further refinement or conversion to pig iron. During sintering of pelletized or balled magnetite concentrates an exothermic conversion of the magnetite to hematite raises the temperature to approximately 2350 F. Although pelletizing or balling is simply an intermediate step in the overall production of iron from low grade ores, the requirements of the unfired pellets or balls are as severe as any of the succeeding firing operations. These green or uncured pellets or balls must possess structural characteristics or properties which enable them to withstand vigorous handling and loading into the pelletizing furnace and travel through the furnace without breakage and they must be of such a coherency to maintain their shape throughout the critical period during firing when moisture is driven off.

Numerous binders will impart varying degrees of some 3,151,972 Patented Oct. 6, I964 of the properties desired in taconite ore or magnetite concentrate pellets or balls, i.e., green strength, dry strength, etc., but for one reason or another conventional binders have failed to fully satisfy a majority of requirements or to fulfill all desired properties.

It is a primary object of this invention to provide an economically feasible means of increasing green or unfired wet strength and handleability of particulate iron oxide ore pellets or balls and improving their dimensional stability, and coherency and thermal shock resistance upon final firing.

it is a further object of this invention to provide a means which permits and/or facilitates the use of coarse sized, flaky or lenticular shaped ores or iron oxide concentrates in a pelletizing or balling process and thereby reduce the degree of grinding normally required.

It is a further object of this invention to provide a means of materially improving the thermal shock resistance of wet pelletized or balled iron oxide ore whereby higher drying and/or sintering temperatures, and more rapid exposure or entry of wet shapes to areas of high or sintering temperatures is permitted.

It is a still further object of this invention to provide a means which permits more rapid and effective pelletizing or balling of taconite ores or magnetite concentrates, increases the size of the resulting pellets or balls, and permits greater latitude or substantially extends the heretofore restricted operable range of necessary water content for pelletizing or balling and subsequent strength, etc., by reducing slumping or fiow characteristics among other undesirable properties.

This invention will be more fully understood and further objects and advantages thereof will become apparent from the hereinafter detailed description.

The foregoing as well as other objects and advantages are achieved by adding a relatively small proportion of a fibrous inorganic or mineral component such as asbestos fiber, shorts or floats, in addition to adjusting the moisture content of the resulting mass, to the particulate ore or iron oxide concentrate prior to pelletizing or balling in a rotary drum. The fibrous mineral material should be included in amounts of at least approximately 1 up to about 10% by weight of the ore concentrate and about 5% by weight of the ore concentrate is normally preferred but exact optimum quantities depend upon the fibrous nature or quality of the additament. Furthermore, the increment of benefit derived from utilizing amounts of fiber substantially greater than 10% is ofiset by the cost thereof and increased, or possibly deleterious adulteration of the ore. The moisture content of the ore or concentrate, or mixture of said ore or concentrate and fiber should be adjusted to approximately 5 to 20% by weight of the total, preferably about 10 to 15%. It should be noted however, that different grades of asbestos fiber include different amounts of an actual fibrous component, the balance comprising fine rock or the like, and since it is the fibrous component which is the elfective ingredient, equivalent amounts of different grades of asbestos often provide results differing in degree. Typically, the properties imparted are directly proportional to the fibrous 3 content of the asbestos added. The fiber and moisture should be substantially uniformly blended with or throughout the ore or iron oxide. Accordingly, other than a small amount of moisture, no bonding agents or 4 the bodies. Moreover, due to the tendency of asbestos fiber or the like to nodulate or ball when rolled, asbestos substantially facilitates the formation of balls or shapes as well as imparting improved stability and coherency components such as clay or the like are necessary or need 5 strength characteristics to said balls or shapes. be included to impart wet strength and coherency or fa- The following examples illustrate suitable taconite ore cilitate pelletizing or balling. However, conventional or magnetite concentrate pellets or balls in approximate binders such as clays may be advantageously incorporated percentages by weight and methods of preparing the same. in the mass in addition to the essential fibrous component It is to be understood that the compositions of the taconite if desired or appropriate. Bentonite clay, for example, ores or magnetite concentrates are neither a part of this is highly effective in imparting high dried or fired pellet invention nor are they to be construed as limiting the strength and may be advantageously utilized with inorsame. Moreover, compositions of the following pellets ganic fiber, which provides high green or wet strength 01" balls are exemplary and not to be construed to limit and thermal shock resistance, among other properties. the invention to the particular ores or other components In addition to both amphibole and chrysotile asbestos specified in the examples. fibers, shorts or floats, the essential fibrous component The ni C ntrat s uti zed in the foll wing eX- may i t f inorganic r mineral fibers including, for amples and tests are identified or composed as follows: p mineral rock wool fibers: glass fibers talc Fine taconite samplea fine magnetic concentrate con- Wollastonite or other fibrous calcium silicates, etc. Ortaming approximately 75% iron as magnetic oxide with gallie fibers Such as cellulose fibers Synthetic resin the balance being largely silica. This material is essenfibrous materials, although they substantially improve tially all below 3 00 mesh. green or Wet strength of the pellets or balls, burn out Coarse taconite samplemixed taconite concentrate conupon firing, resulting in very porous, flaky shapes. Moretaining approximately 70.5% iron in the form of magover, fibrous asbestos materials are highly preferred in that ll'etie OXide and a total Silica nt f 1% Th s matethey not only substantially improve green or wet strength Tlal has about 12% greater than 100 mesh granules and and dimensional stability of the shapes but asbestos mateabout 21% below 325 mesh' rially enhances or facilitates the pelletizing or balling E l ti d comparison f h d fi d process by readily disp s ng i e s and fostering strength of coherency and thermal shock resistance of orma o and retention of the Shapes, Whereas fibrous wetted taconite concentrates shaped both with and without materials comprising mineral or rock, glass, cellulose, a b to was ar i d out as follow synthetic resins or the like are diflicult to disperse in and Sta d d Tiniu Ol n e ent mold were u ed to form mix with ores to provide satisfactory blends. taconite or magnetite concentrate containing dumbbell Handleable or workable pellets or the like shapes comha ed samples of mixes composed of the ingredients set prising particulate ore or concentrate, asbestos fiber or f th i th following t bl Molding was fi t d i the like inorganic fiber and moisture y be readily ply by completely filling each mold with the wetted mass, formed by consolidating a substantially uniform blend of levelin and smoothing the upper or exposed surface of the same in a press, casting in a mold, or, blending and each molded shape with a spatula. The wetted materials shaping said components in a rotary drum, i.e., subjecting were permitted to air dry for about 1 hour before releasing said materials to the action of a rotating drum or cylinder from the mold. After removing the mold, each sample until they are rolled or agglomerated into a plurality of was allowed to air dry an additional 3 hours before placing strong, handleable nodules or balls. This latter procedure, it in an 1800 F. mufile furnace for 1 hour. The test data balling, is typical of taconite refining techniques of shaping are given in the following tables:

EXAMPLE I Table 1.Tests on Molded T aconite Concentrate Specimens Mix Proportions Visual Observations and Comments Taconite Asbestos Used Fiber Percent Percent Percent In Wettcd Condition Used Taconite Asbestos Water After Firing 1 hr. at 1800 F.

Fiber Added 7 In Mold After Mold Released Fine None.... 100 0 15 Verywet,fre e water onsurface slumped, deformed, couldnot Very badly crumbled, only after molding. be handled. about original size. Do 6D20 5 15 Relatively dry, no evidence of Handleable, supportedits own Cracks and flaking on surface, water on surface. weight, no slumping. but no serious breakdown.

Retained shape. Do None 0 7% Drier than Test 1, no free Did not slump or deform, but Disintegrated in much the water. figyd weak. Broke when same as Test 1.

Do 7RF1 95 5 15 Similar to Test 2 No slump, could be handled Surface cracks and minor flakand supported its own ing, but retained full shape weight. with no crumbling.

Coarse--- None 100 0 15 Extremely wet water on Well formed, did not slump, Disintegrated around edges surface. weak, broke in handling. andr Cllinbled. Not as bad as es Do 6D20 95 5 15 Drier than Test 5, but molded Well formed, easily handled, Absolutely no deformation,

eas1ly. arndt fmuch stronger than cracking, or crumbling.

EXAMPLE II Table 2.Efiect of Various Fibrous Materials on Properties of Molded Fine Taconz'te Concentrate Specimens Fired at 1800" F.

Visual Observations and Comments Percent Percent Type of Fiber Fiber in Water During Molding in Wetted Condition Mix Added During Mixing After 1 hr. at

1800 In Mold After Mold Release None None 15 Mixed easily Very wet, free water on Slumped, deformed, Very badly crumbled, 7 surface. could not be handled. only about 56 original size.

Rock wool 5 15 Mixed poorly, not ho- Fairly dry, but some No slumping, but poor- No shape distortion.

mogeneous. Water visible on surly formed. Bottom Minor surface crackface. porous. Supported ing.

its weight.

Glass wool 5 15 Extremely poor mixing, Fairly dry. considerable N slumping, handle- No shape distortion. definitely not homoevidence of unmixed able, supported its Minor surface flaking. geneous. fiber. weight.

Sulfite pulp 30 Fair mixing, but lumpy. Mix very wet,abundant No slumping, handle- Caught fire, leaving very water on surface. able. porous, flaky briquette. Do 5 Poor Imxing, lumpy. Mix very dry, poor sur- No slumping, slight Caught fire, leaving poface. cracking during hanrous briquette which dlmg. flaked on handling.

Asbestos (7RF1) 5 15 Mixed easily, no fiber Moistsurfacebut no free No slumping, complete- No shape distortion, visible. water on surface. ly handleable, supvery minor surface ported its weight. cracks.

Asbestos (SD) 5 15 Mixed easily Relatively dry, no sur- No slump, supported No shape distortion,

face water. its own weight, hanminor surface cracks.

dleable.

EXAMPLE III Table 3.Efiect of Asbestos Concentration Upon Properties of Molded Fine Taconite Concentrate Specimens Fired at 1800 F.

[15% water added in all tests] Visual Observations and Comments Asbestos Percent During Molding in Wetted Condition Fiber Fiber Briquctte in Mix During Mixing After Firing 1 hr. at 1800 F. Weight,

Briquette In Mold After Mold Release Wet wt,

None--- 0 Mixed easily Very wet, free water on Slumped,deformed,could (1) Very badly crumbled, only (1) surface. not be handled. about original size.

FRF1 1 Mixed easily, Moist, but not excessively Soft and plastic, but no 193 Flaked badly, but retained 172 uniform. wet. slump, supports weight about of shape.

in tension but not flexure. 7RF1 3 do Drier than tests Slightly soft, no slump, 195 Very good stability com- 173 definitely handleable pared with Test 5. Slight and supported weight. surface flaking but shape retained. 7RF1 5 do Surface moist but no ex- No slump, completely 189 No shape distortion, very cess water on surface. l candlealliilze, supported minor surface cracks.

1 5 won; 7RFl 10 Very dry mix, Moldedsatisfactorily,sur- Very strong, no slump, 179 Absolutely no evidence of 168 balls formed. face very dry. very easily handleable, distortion or surface cracksupported own weight ing or flaking. with ease. 6D20 1 Mixed easily, Moist, but no iree water Soft, but did not break in Good shape stability, defi- 173 uniform. or excessive moisture. handling, definitely nitely superior to Test 5.

stronger than Test 5. Minor surface cracking. 6D20 3 do dn No slump, supported own 193 Excellent shape stability, 171

weight easily without very minor surface cracks. cracking. SD20..-" 5 do Relatively dry no surface No slump, supported its No shape distortion, minor water. own weight, easily han' surface cracks.

dleable.

l Not taken.

In Example I the addition of asbestos fiber to taconite ore or concentrates substantially improved the wet strength of the molded pellets or balls. In all cases, the wet samples formed without fiber were so weak and soft that they could not support their own weight. Additions of 5% 7RF1 or 5 6D20 asbestos fiber improved the wet strength of these samples to such a degree that they could be very easily handled and readily supported their own weight. The dimensional stability and thermal shock resistance of the wettcd taconite or magnetite concentrate samples prior to firing was also vastly improved by the addition of asbestos fiber. This was particularly true in the case of the fine (325 mesh) material in which case the fiberless molded piece began to slump and deform immediately after the restraining mold was released. This did not occur when asbestos fiber or asbestos floats were incorporated with the fine magnetic concentrate. The effect of asbestos fiber upon the dimensional stability of the molded samples when fired at 1800 F. was extremely startling. Without the inclusion of asbestos, the items molded from both the fine and coarse taconite concentrates immediately began to disintegrate when placed in the furnace. This was undoubtedly due to the rapid escape of the moisture from the samples. As the moisture was driven off, minor explosions occurred on the surface of the sample until it finally crumbled into a shapeless mass. However, with the inclusion of asbestos fiber in the form of 7RF1 or 6D20 at the 5% level, the molded samples showed an outstanding improvement in dimensional stability. In the case of the fine (325 mesh) concentrate, surface cracks appeared onthe topof the samples, but there was only a relatively minor flaking of the surface and no crumbling. In all cases, samples containing asbestos fiber retained their original shape and integrity in contrast with the samples prepared without asbestos fiber. This was true despite the fact that under these firing conditions (1800 F.) asbestos fiber loses almost all of its strength and becomes brittle.

Example II illustrates the effect of inorganic or mineral fiber other than asbestos as well as organic fibrous materials. Other than asbestos, both inorganic and organic fibrous materials were difiicult to disperse and mix with the ore concentrates. However, once mixed the inorganic fibers imparted good green or Wet strength, shape retention and resistance to thermal shock. Organic fiber containing pellets, though exhibiting good green or wet strength, failed to satisfactorily endure firing.

It will be understood that the details given are for the purposes of illustration, not restriction, and that variations within the spirit of this invention are intended to be included in the scope of the appended claims.

What I claim is:

1. A method of pelletizing particulate iron oxide ore concentrates comprising binding the particulate ore with 8 the steps of combining with the iron oxide ore concentrates asbestos fiber in amount of approximately 1 to 10% by'weight of said ore, adjusting the moisture content of the combined mass to approximately 10 to 15% by weight of the total, and pelletizing the mass.

3. A method of pelletizing particulate iron oxide concentrates comprising binding the particulate ore with inorganic fiber, said method consisting essentially of the steps of combining with the iron oxide ore concentrates asbestos fiber in amount of approximately 1 to 10% by weight of said ore, adjusting the moisture content of the combined mass to approximately 5 to 20% by weight of the total, and balling the mixture in a rotary ball drum.

4. An ore pellet for use in a blast furnace which consists essentially of particulate iron ore concentrates bonded with approximately 1 to 10%, by weight of said iron ore concentrates, of asbestos fiber together with moisture in amount of approximately 5 to 20% by weight of the total mass.

5. A fused ore pellet comprising thermally reacted particulate iron ore concentrates bonded with approximately 1 to 10%, by weight of said iron ore concentrates, of asbestos fiber together with moisture in amount of approximately 10 to 15% by weight of the total mass.

References Cited in the file of this patent UNITED STATES PATENTS 2,411,873 Firth Dec. 3, 1946 2,446,990 Schuetz Aug. 10, 1948 2,559,572 Stalego July 3, 1951 2,592,521 Thompson Apr. 8, 1952 2,693,668 Slayter Nov. 9, 1954 2,865,731 Crowe Dec. 23, 1958 2,870,689 Brennan Jan. 27, 1959 

1. A METHOD OF PELLETIZING PARTICULATE IRON OXIDE ORE CONCENTRATES COMPRISING BINDING THE PARTICULATE ORE WITH INORGANIC FIBER, SAID METHOD CONSISTING ESSENTIALLY OF THE STEPS OF COMBINING WITH THE IRON OXIDE ORE CONCENTRATES ASBESTOS FIBER IN AMOUNT OF APPROXIMATELY 1 TO 10% BY WEIGHT OF SAID ORE, ADJUSTING THE MOISTURE CONTENT OF THE COMBINED MASS TO APPROXIMATELY 5 TO 20% BY WEIGHT OF THE TOTAL, AND PELLETIZING THE MASS. 